The ultraviolet variations of the post-AGB star HD 89353

Abstract

Based on an analysis of all low resolution spectra of HD 89353 (HR 4049) obtained with the International Ultraviolet Explorer (IUE) over several years and uniformly reprocessed, we report on large ultraviolet variations for this star whose amplitude increases towards long wavelengths. Ultraviolet maximum and minimum occur respectively at phase 0.52 and 0.92 of Waelkens et al. (1991) ephemeris which suggests that ultraviolet and optical variations occur in phase. The ultraviolet energy distribution of HD 89353 is very deficient compared to that of the standard A6Ib star, HD 80404, and compared to the predictions of an ATLAS 9 model (Teff = 7500K, log g = 2.0 and [M/H]= -5.0) which bests fit the optical continuum. The ultraviolet flux deficiency scales as <~mbda(-1) , a trend already noted earlier (Waelkens et al. 1995). The most likely interpretation is that variable circumstellar extinction drives the ultraviolet and optical variations as proposed by Waelkens et al. (1991). Based on data from the International Ultraviolet Explorer .